RECENT PROGRESS IN ELECTRICITY. 
173 
eddy currents. Now, in the case of the old attracted pole 
motor, lamination would be beneficial, whilst in the induc¬ 
tion motor, since it is solely by these induced currents that 
the motor operates, lamination would absolutely prevent in¬ 
ductive working in the case of motor armatures such as those 
shown in the patent drawings. Thus careful perusal of the 
original patent applications shows without possibility of con¬ 
tradiction that the idea of an induction motor was entirely 
foreign to Tesla’s invention, which was, as he himself de¬ 
scribes it, the employment of alternating currents instead of 
commutated direct currents in a revolving pole motor, of the 
old type, for the purpose of preventing sparking. 
It is to Ferraris, of Italy, that the invention of the induc¬ 
tion motor is due. He worked out the problem and gave 
the correct theory about the same time that Tesla was work¬ 
ing on the problem, but was unfortunately misled into the old 
pitfall of the confusion between maximum amount of energy 
output and maximum efficiency (the same mistake which 
retarded the use of-the direct-current motor) into stating 
that the motor was not commercial, as it wasted half the 
energ}L 
Temporarily the motor was dropped out of sight for a few 
years, but was meantime being developed energetically in 
Germany, and also by the engineers of the Westinghouse 
Company in this country. Gradually it was developed, as 
its theory became better understood, and its many advan¬ 
tages gave it a large sale. 
The problem of the alternating current motor for single 
phase was still, however, unsolved. Devices, such as splitting 
the current, were tried, but without success, except for cer¬ 
tain limited cases. It was found that two and three phase 
motors would run on single-phase circuits, but under these 
conditions the}^ could be made to have but very little start¬ 
ing torque, and were heavier for their output. Finally, 
Steinmitz, by using polyphase motors on a single phase, with 
proper inductances and capacities in the motor circuits, 
evolved a motor which was the complete solution to the 
